Method of making a heat exchanger

ABSTRACT

A method of making a heat exchanger that includes sealing tubes to header slots and brazing the tubes to the header slots. The method further includes coupling a cover to the header to cover a liquid-side surface of the header and to cover ends of the tubes, and applying flux to an air-side surface of the header and to the tubes. Coupling the cover to the header is performed after sealing the tubes to the header slots and coupling the cover to the header is performed before applying flux to the air-side surface of the header and to the tubes. Applying flux is performed before brazing each of the tubes to the header slots and sealing each of the tubes to the header slot includes sealing a perimeter of each of the tubes to the header slot.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/411,712, filed Aug. 25, 2021, which claims priority to U.S.Provisional Patent Application No. 63/070,569, filed Aug. 26, 2020, theentire contents of which are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to heat exchangers and to a method ofmaking heat exchangers.

BACKGROUND OF THE INVENTION

Heat exchangers include components like tubes, headers, and fins thatare joined together in a brazing process. Flux is commonly applied tothe heat exchanger components prior to the brazing process to ensure ahigh quality, brazed joints between the heat exchanger components. Thefluxing process commonly includes dipping an assembled heat exchangerinto a flux composition or spraying the flux composition around theassembly heat exchanger. The fluxing process can be messy, and, it maybe undesirable to have a significant amount of flux remaining in areasof the heat exchanger. Often, the heat exchanger assembly is cleaned ator near the end of the production of the heat exchanger to at leastpartially remove flux.

SUMMARY OF THE INVENTION

The present invention provides, in one aspect, a method of making a heatexchanger. The method comprises arranging a plurality of tubes in aformation, coupling the plurality of tubes to a header, includingsealing each of the tubes of the plurality of tubes to a header slot ofa plurality of header slots in the header and brazing each of the tubesof the plurality of tubes to said header slot of the plurality of headerslots, coupling a cover to the header to cover a liquid-side surface ofthe header and to cover ends of the tubes, and applying flux to anair-side surface of the header and to the plurality of tubes, whereincoupling the cover to the header is performed after sealing each of thetubes of the plurality of tubes to said header slot of the plurality ofheader slots, wherein coupling the cover to the header is performedbefore applying flux to the air-side surface of the header and to theplurality of tubes, wherein applying flux is performed before brazingeach of the tubes of the plurality of tubes to said header slot of theplurality of header slots, and wherein sealing each of the tubes of theplurality of tubes to said header slot includes sealing a perimeter ofeach of the tubes to said header slot.

In some embodiments, the tank is coupled to the header via crimping.

In some embodiments, the step of coupling ends of each of the pluralityof tubes to a liquid-side surface of the header includes welding each ofthe plurality of tubes to the liquid-side surface of the header.

In some embodiments, the method further comprises a step of placing aheader onto the plurality of tubes after arranging the plurality oftubes in a formation.

In some embodiments, the step of coupling the cover to the header tocover the liquid-side surface and the ends of the tubes is performedprior to the step of applying flux to the plurality of tubes adjacentthe air-side surface of the header and to the header.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a heat exchanger.

FIG. 2 is a flowchart illustrating assembly of the heat exchanger ofFIG. 1.

FIG. 3 is a partial perspective exploded view of the heat exchanger ofFIG. 1.

FIG. 4 is a perspective view of tubes being welded to a header of theheat exchanger of FIG. 1.

FIG. 5 is a partial exploded view of the heat exchanger of FIG. 1.

FIG. 6 is an enlarged cross-sectional view of the heat exchanger of FIG.1.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

DETAILED DESCRIPTION

FIG. 1 illustrates a heat exchanger 10 including a first collection tankassembly 14 and a second collection tank assembly 18. The firstcollection tank assembly 14 includes a header 22 and a collection tank26 with an inlet 30. The second collection tank assembly 18 includes aheader 34 and a collection tank 38 with an outlet 42. In someembodiments, each of the headers 22, 34 are aluminum with braze claddingon one or two sides thereof. In some embodiments, the collection tanks26, 38 are formed of plastic and in such embodiments, gaskets arerespectively arranged between the collection tanks 26, 38 and theirrespective headers 22, 34. In some embodiments, the collection tanks 26,38 are made from aluminum and brazed to the headers 22, 34. A pluralityof tubes 46 fluidly couple the first and second collection tankassemblies 14, 18 and are coupled to the headers 22, 34 of the first andsecond collection tank assemblies 14, 18. In some embodiments, the tubes46 are formed of aluminum with braze cladding on one or two sides. Insome embodiments, the tubes 46 are welded, but in other embodiments,could be folded. In some embodiments, the tubes 46 have cladding on bothsides of the tubes. Fins 47 are disposed between tubes 46, and the fins47 are formed of aluminum with no cladding. Side plates 56, as shown inFIG. 3, are located at ends of the heat exchanger 10. The side plates 56are formed from aluminum with cladding on one or both sides of the sideplates 56. The side plates 56 are each joined to one of the fins 47.

In operation of the heat exchanger 10, a liquid (e.g. water and/orcoolant) flows into the inlet 30 of the collection tank 26 at arelatively high temperature, and then flows through the tubes 46 to thecollection tank 38, before flowing out the outlet 42. While flowingthrough the tubes 46, the liquid is cooled, as heat escapes the liquidvia the tubes 46, which are typically cooled by airflow. In someembodiments, the heat exchanger is used to coolant for fuel cellcooling, and in such instances, the coolant is required to have lessimpurities, such as flux residues.

FIG. 2 illustrates a method 50 of making the heat exchanger 10, or atleast the first collection tank assembly 14 and/or the second collectiontank assembly 18 of the heat exchanger 10. For simplicity ofdescription, the following explanation will just cover the making of thefirst collection tank assembly 14. First, as shown at step 54, the tubes46 arranged in an array, stack, or formation in which they will becoupled to the header 22. During step 54, the side plate 56 is on thebottom of the stack and an opposite side plate 56 is on the top of thestack. One of the fins 47 is next to each of the side plates 56. Thestack is completed by alternating fins and tubes 46.

At step 58 and as shown in FIG. 3, the header 22 is placed onto thetubes 46 by inserting the tubes 46 through slots 60 in the header 22. Atstep 62, ends 66 of the tubes 46 are welded to the header 22 on aliquid-side surface 70 (FIG. 3), thereby blocking flux from penetratingthe header 22 to contact the liquid-side surface 70 or the ends 66 ofthe tubes 46. FIG. 4 illustrates an example process of welding the tubes46 to the header 22, using a multi-torch welder 74. No braze filler orback solder is applied between the tubes 46 and the respective headers22, 34, as the engaged surfaces are clad with braze material thatultimately melts to join the tubes 46 to the respective headers 22, 34.The slots 60 have collars that extend to the inside of the header 22.These collars have a thinner wall than the nominal thickness of theheader 22, being thinned as they are formed. In some embodiments, thecollars are formed such that they are thinner than the nominal thicknessof the material forming the header 22. Ideally, the thickness of thecollar material would equal the thickness of the tube material. Thecollar extends in a direction towards the interior of the header 22.

During step 62, the production line includes a welder on one side of theproduction line, which could be a torch welder as shown in FIG. 4, orcould be other types of conventional welders. The production line couldinclude welders are both sides of the production line. As the header 22and tubes 46 stops at the welder location, the welder welds the tubes 46to the header 22. For a production line with a welder on just one side,the header 22 must be rotated to weld tubes 46 to the header 22 on theopposite side. For a production line with welders on both sides, thetubes 46 can be welded to the headers 22 on both sides of the header 22at the same time. The geometry of the slot 60 in the header 22 helps tocreate the weld between the tube 46 and the header 22. The insertiondistance of the tubes 46 into the header 22 is such that the ends of thetubes 46 extend through the header 22 and beyond the edges of thecollars. The welding process melts both the ends of the tubes 46 andpart of the collars to create a weld bead completely around the tubeslot 60, sealing the tubes 46 to the tube slots 60.

In some embodiments, the welder includes a torch head, which can movealong in predetermined pattern, and the torch head includes a pluralityof torches. The pattern is programmed such that at least one torch movesaround the perimeter of each tube 46 or collar during welding of thetube 46 to the collar. The torch may also follow a pattern that crossesa nose area (the narrow end of the tube) of the tube 46 at least onetime in each nose area of the tube 46 and, ideally, multiple times. Theweld pattern at the nose areas may look like an “X”. The purpose of theweld at step 62 is to completely seal the tube 46 to the header 22around the tube slot 60. The weld bead will be located either flush withthe inside of the header 22 to 2-3 mm from the inside wall of the header22.

At step 86, a temporary cover 90 is coupled over the header 22, therebycovering the liquid-side surface 70 and the ends 66 of the tubes 46welded to the header 22. During step 86, the temporary cover 90 extendscompletely over the header 22, around the perimeter of the header 22,and overlaps the side walls of the header 22 on the outside of the sidewalls. In some embodiments, the temporary cover 90 fits inside of theheader 22, completely covering the inside of the header 22 and the ends66 of the tubes 46, and overlaps the side walls of the header on theinside of the side walls. In another embodiment, instead of thetemporary cover 90, the collection tank 26 is brazed to the header 22during the brazing operation. The temporary cover 90 can be made fromplastic or metal. The temporary cover 90 can be fastened to the headerby an interference fit, snap-on fit, clamps, straps, or a mechanicalfixture having a geometry that engages with both the header 22 and thetemporary cover 90.

At step 94, flux is applied to the tubes 46, fins 47, side plates 56,and the surfaces of the header 22 that face the tubes 46. The fluxremoves oxidation on these surfaces during a subsequent brazing process,thus preventing corrosion and promoting the free flow brazing materialfrom the braze cladding. Because the temporary cover 90 covers theliquid-side surface 70 and the ends 66 of the tubes 46 are welded to theheader 22 prior to the application of flux at step 94, contamination ofthe tube, which can sometimes occur during application of flux, isinhibited. Thus, subsequent contamination of the liquid, such as fuelcell coolant, when passing through the tubes 46, is inhibited. In someembodiments, the temporary cover 90 is removed from the header 22 afterfluxing and before brazing, particularly when the temporary cover 90 isformed from a plastic material.

At step 98, the header 22 goes through a brazing process while thetemporary cover 90 remains on the header 22. During step 98, the brazingmaterial of the braze cladding melts to join the tubes 46 to the header22 at the air-side surface 82, thereby forming a braze fillet 102 (FIG.6) at the air-side surface 82, which further strengthens the jointsbetween the tubes 46 and the header 22. In some embodiments, the heatexchanger 10 is moved into the brazing furnace, which is for aControlled Atmosphere Brazing (CAB) process. In the brazing process, theclad materials melt from the heat of the furnace, and the base materialsof the components do not melt. The clad materials flow to joint areasbetween components. The joint areas are where the tubes 46 meets theheader 22 at the air-side surface of the header 22, where the tubes 46meet the fins 47, and where the fins 47 meet the side plates 56. As theheat exchanger assembly 10 is removed from the furnace, the cladmaterial cools and forms joints in these areas. In some embodiments, thecollection tank 26 is brazed to the header 22 to form heat exchangertanks. In some embodiments, unwanted debris will be brazed to the insidecladding of the tube 46 (for tubes 46 with cladding on both sides-theinside clad for removing debris) during the brazing process to provide acleaner tube volumes.

At step 106, the temporary cover 90 is removed from the header 22. Atstep 110, to replace the temporary cover 90, the collection tank 26 iscoupled to the header 22 via, e.g., crimping. In some embodiments, thecollection tank 26 is stainless steel and is snapped onto the header 22.When the collection tank 26 is coupled to the header 22, a gasket isarranged between the collection tank 26 and the header 22.

In an alternative embodiment, the collection tank 26 is coupled to theheader 22 at step 86, instead of the temporary cover 90. In thisalternative embodiment, the collection tank 26 remains on during step94, thereby inhibiting contamination of the tubes 46. Also in thisalternative embodiment, the collection tank 26 is removed prior to step98, such that the collection tank 26 (which can be formed of plastic)does not melt during the brazing process. After the brazing process atstep 98, the collection tank 26 would then be recoupled to the header22.

In some embodiments, the heat exchanger 10 is part of a fuel cell andthe liquid is fuel cell coolant. In some embodiments, instead of weldingthe ends 66 of the tubes 46 to the liquid-side surface 70 of the header22, the slots 60 in the header 22 are packed with a sealant, whichprevents the flux from entering the header 22 and contacting theliquid-side surface 70. The sealant then dissolves in the brazingprocess. In some embodiments, the collection tanks 26, 38 are aluminumwith cladding on one or two sides, and the collection tanks 26, 38 arebrazed to the headers 22, 34 during the brazing step 98 of the method50.

Although the invention has been described in detail with reference tocertain preferred embodiments, variations and modifications exist withinthe scope and spirit of one or more independent aspects of the inventionas described.

What is claimed is:
 1. A method of making a heat exchanger, the methodcomprising: inserting each of a plurality of tubes into respectiveheader slots of a header, wherein each of the plurality of tubes and theheader include braze cladding; welding ends of each of the plurality oftubes into the respective header slots on a liquid side surface of theheader such that perimeters of each of the plurality of tubes are sealedinto their respective header slots by welding the perimeter of each ofthe tubes to their respective header slot at the liquid-side surface ofthe header; coupling a cover to the header to cover a liquid-sidesurface of the header and to cover ends of each of the plurality oftubes; applying flux to an air-side surface of the header and to theplurality of tubes, the flux configured to remove oxidation from areaswhere the flux is applied, and brazing each of the plurality of tubes totheir respective header slots such that the braze cladding is melted toform a braze fillet on the air-side surface of the header between eachof the plurality of tubes and the header, wherein the welding of theends of each of the plurality of tubes into the respective header slotson a liquid side surface of the header is configured to block flux frompenetrating the header to contact (i) the liquid side surface of theheader and (ii) the ends of each of the plurality of tubes; whereincoupling the cover to the header is performed before applying flux tothe air-side surface of the header and to the plurality of tubes, andwherein applying flux is performed before brazing each of the pluralityof tubes to their respective header slots.
 2. The method of claim 1,wherein the cover, when coupled to the header, extends completely overthe header, around the perimeter of the header, and overlaps sidewallsof the header.
 3. The method of claim 1, wherein the tubes are insertedinto the header slots such that the ends of the tubes extend beyondflanges formed around each of the header slots, wherein the flangesextend from the liquid-side surface of the header.
 4. The method ofclaim 3, wherein the tubes are inserted into the header slots such thatthe ends of the tubes are parallel to the edges of the flanges.
 5. Themethod of claim 1, wherein the cover is removed after the step ofbrazing each of the plurality of tubes to respective header slots of theplurality of header slots.
 6. The method of claim 1, wherein the coveris removed after the step of applying flux to the air-side surface ofthe header and to the plurality of tubes.
 7. The method of claim 6,wherein the cover is removed before the step of brazing each of thetubes of the plurality of tubes to their respective header slot.
 8. Themethod of claim 1, further comprising: removing the cover from theheader; assembling a gasket onto the liquid-side of the header after thecover is removed; and assembling a tank to the header after the gasketis assembled onto the liquid-side of the header.
 9. The method of claim1, wherein the step of coupling the cover includes removably clampingthe cover to side plates of the heat exchanger or welding the cover tothe header.
 10. A method of making a heat exchanger, the methodcomprising: arranging each of a plurality of tubes in respective headerslots of a header; coupling a cover to the header to cover a liquid-sidesurface of the header and to cover ends of each of the plurality oftubes; applying flux to an air-side surface of the header and to theplurality of tubes, and brazing each of the plurality of tubes to theirrespective header slots, wherein coupling the cover to the header isperformed before applying flux to the air-side surface of the header andto the plurality of tubes, and wherein applying flux is performed beforebrazing each of the plurality of tubes to their respective header slots.11. The method of claim 10, wherein perimeters of each of the pluralityof tubes are sealed into their respective header slots by welding theperimeter of each of the tubes to their respective header slot at theliquid-side surface of the header.
 12. The method of claim 11, whereinsealing each of the plurality of tubes to said header slot includespacking a sealant around the perimeter of each of the tubes and betweeneach of the tubes and their respective headers slots.
 13. The method ofclaim 10, further including forming header slots into the header byforming a flange around each of the header slots, wherein the flangeextends from the liquid-side surface of the header.
 14. The method ofclaim 13, further including forming an edge of the flange to a have anedge thickness, wherein the edge thickness is less than a headerthickness and greater than or equal to a tube thickness.
 15. The methodof claim 14, wherein the edge thickness is formed to equal the tubethickness, wherein the tubes are inserted into the header slots suchthat the ends of the tubes extend beyond edges of the flanges, andwherein the tubes are inserted into the header slots such that the endsof the tubes are parallel to the edges of the flanges.
 16. The method ofclaim 10, wherein the cover is removed after the step of applying fluxto the air-side surface of the header and to the plurality of tubes. 17.The method of claim 10, wherein the cover is removed after the step ofbrazing each of the tubes of the plurality of tubes to said header slotof the plurality of header slots.
 18. The method of claim 17, wherein atank is assembled to the header after the cover is removed.
 19. Themethod of claim 16, wherein the cover is removed before the step ofbrazing each of the tubes of the plurality of tubes to said header slotof the plurality of header slots.
 20. The method of claim 19, wherein atank is assembled to the header after the cover is removed.